1. Field of the Invention
This invention relates to acoustics, in particular, to fluid-conducting mufflers combined with pneumatic devices.
2. Description of the Prior Art
Spent working fluid from impulsive motion and impacts of air-operated hand tools and other pneumatic devices is a major source of in-plant noise pollution. Due to the present national concern about noise pollution, the U.S. Congress enacted the Occupational Safety and Health Act (hereinafter OSHA), effective April, 1971. Thereunder, the U.S. Department of Labor promulgated regulation 1910.95 in 39 Federal Register 23596 (June 27, 1974). The regulation governs the permissible noise exposure for employees inside a plant and requires that engineering controls be utilized to reduce sound levels below stated limits. For example, the noise exposure for employees over an eight hour period should not exceed 90 decibels on the A scale of a standard sound level meter at slow response (hereinafter dBAs). Many unmuffled air-operated hand tools and other pneumatic devices are not in compliance with this OSHA regulation. Many attempts to muffle such tools and pneumatic devices have been unsatisfactory because of icing up of the vents or a significant reducing in operating efficiency of the tools and pneumatic devices.
Exemplary prior art rubber mufflers designed for specific pneumatic devices are shown and described in U.S. Pat. Nos. 2,152,205, 3,225,861, 3,459,275 and 3,554,316. Exemplary non-elastic mufflers are shown and described in East German Pat. No. 47,382, British Pat. No. 810,398, and U.S. Pat. Nos. 3,891,049 and 3,993,159.
However, it is still a problem in the acoustic art to manufacture a cheap, easily manufactured, effective, unitary, elastic muffler assembly for reducing the noise level of air-operated hand tools and other pneumatic devices below the 90 dBA level without icing up or reducing significantly the efficiency of such tools and devices and for telescopingly engaging tubular housings of variously sized air-operated hand tools and other pneumatic devices.